The present invention is directed to aqueous ink compositions. More specifically, the present invention is directed to ink compositions suitable for use in ink jet printing processes. One embodiment of the present invention is directed to an ink composition which comprises water, a colorant, and a monomeric oxazolidinone compound.
Ink jet printing systems generally are of two types: continuous stream and drop-on-demand. In continuous stream ink jet systems, ink is emitted in a continuous stream under pressure through at least one orifice or nozzle. The stream is perturbed, causing it to break up into droplets at a fixed distance from the orifice. At the break-up point, the droplets are charged in accordance with digital data signals and passed through an electrostatic field which adjusts the trajectory of each droplet in order to direct it to a gutter for recirculation or a specific location on a recording medium. In drop-on-demand systems, a droplet is expelled from an orifice directly to a position on a recording medium in accordance with digital data signals. A droplet is not formed or expelled unless it is to be placed on the recording medium.
Since drop-on-demand systems require no ink recovery, charging, or deflection, the system is much simpler than the continuous stream type. There are two types of drop-on-demand ink jet systems. One type of drop-on-demand system has as its major components an ink filled channel or passageway having a nozzle on one end and a piezoelectric transducer near the other end to produce pressure pulses. The relatively large size of the transducer prevents close spacing of the nozzles, and physical limitations of the transducer result in low ink drop velocity. Low drop velocity seriously diminishes tolerances for drop velocity variation and directionality, thus impacting the system's ability to produce high quality copies. Drop-on-demand systems which use piezoelectric devices to expel the droplets also suffer the disadvantage of a slow printing speed.
The other type of drop-on-demand system is known as thermal ink jet, or bubble jet, and produces high velocity droplets and allows very close spacing of nozzles. The major components of this type of drop-on-demand system are an ink filled channel having a nozzle on one end and a heat generating resistor near the nozzle. Printing signals representing digital information originate an electric current pulse in a resistive layer within each ink passageway near the orifice or nozzle, causing the ink in the immediate vicinity to evaporate almost instantaneously and create a bubble. The ink at the orifice is forced out as a propelled droplet as the bubble expands. When the hydrodynamic motion of the ink stops, the process is ready to start all over again. With the introduction of a droplet ejection system based upon thermally generated bubbles, commonly referred to as the "bubble jet" system, the drop-on-demand ink jet printers provide simpler, lower cost devices than their continuous stream counterparts, and yet have substantially the same high speed printing capability.
The operating sequence of the bubble jet system begins with a current pulse through the resistive layer in the ink filled channel, the resistive layer being in close proximity to the orifice or nozzle for that channel. Heat is transferred from the resistor to the ink. The ink becomes superheated far above its normal boiling point, and for water based ink, finally reaches the critical temperature for bubble formation or nucleation of around 280.degree. C. Once nucleated, the bubble or water vapor thermally isolates the ink from the heater and no further heat can be applied to the ink. This bubble expands until all the heat stored in the ink in excess of the normal boiling point diffuses away or is used to convert liquid to vapor, which removes heat due to heat of vaporization. The expansion of the bubble forces a droplet of ink out of the nozzle, and once the excess heat is removed, the bubble collapses on the resistor. At this point, the resistor is no longer being heated because the current pulse has passed and, concurrently with the bubble collapse, the droplet is propelled at a high rate of speed in a direction towards a recording medium. The resistive layer encounters a severe cavitational force by the collapse of the bubble, which tends to erode it. Subsequently, the ink channel refills by capillary action. This entire bubble formation and collapse sequence occurs in about 10 microseconds. The channel can be refired after 100 to 500 microseconds minimum dwell time to enable the channel to be refilled and to enable the dynamic refilling factors to become somewhat dampened. Thermal ink jet processes are well known and are described in, for example, U.S. Pat. No. 4,601,777, U.S. Pat. No. 4,251,824, U.S. Pat. No. 4,410,899, U.S. Pat. No. 4,412,224, and U.S. Pat. No. 4,532,530, the disclosures of each of which are totally incorporated herein by reference.
U.S. Pat. No. 5,300,143 (Schwarz), the disclosure of which is totally incorporated herein by reference, discloses an ink composition which comprises water, a water soluble dye, a first component selected from the group consisting of sulfones and mixtures thereof, and a second component selected from the group consisting of cyclic amines having at least one hydrogen atom bonded to a nitrogen atom, cyclic amides having at least one hydrogen atom bonded to a nitrogen atom, diamides having at least one hydrogen atom bonded to a nitrogen atom, polyalkoxy-substituted amides having at least one hydrogen atom bonded to a nitrogen atom, polyimine-substituted amides having at least one hydrogen atom bonded to a nitrogen atom, and mixtures thereof. Also disclosed is an ink jet printing process employing these inks.
U.S. Pat. No. 5,223,026 (Schwarz), the disclosure of which is totally incorporated herein by reference, discloses a thermal ink jet printing process which comprises incorporating into a thermal ink jet printing apparatus an ink composition comprising a colorant and a liquid vehicle which comprises a mixture of water and an organic component selected from the group consisting of cyclic amides, cyclic esters, polyethoxy-substituted or polyimine-substituted amides, and mixtures thereof, and heating selected nozzles in the printing apparatus containing the ink, thereby causing droplets of the ink to be ejected in an imagewise pattern onto a substrate.
Organic solvents and humectants included in ink jet ink compositions have a number of requirements, including water miscibility, thermal stability, hydrolytic stability, low volatility, high boiling point, high surface tension, low viscosity, compatibility with colorants, and the like. Glycols and glycol derivatives are the most widely used solvents and humectants; these materials, however, tend to result in formation of ink compositions with undesirably high viscosities, resulting in less than optimum frequency response and latency when the inks are used in ink jet printing processes. Latency in particular becomes a more critical issue with the introduction of printheads having small channels and relatively high values of dots per inch.
Accordingly, while known compositions and processes are suitable for their intended purposes, a need remains for improved ink compositions suitable for use in ink jet printing processes. In addition, a need remains for ink compositions suitable for ink jet printing containing solvents or humectants with high water miscibilities. Further, a need remains for ink compositions suitable for ink jet printing containing solvents or humectants with high thermal stabilities. Additionally, a need remains for ink compositions suitable for ink jet printing containing solvents or humectants with high hydrolytic stabilities. There is also a need for ink compositions suitable for ink jet printing containing solvents or humectants with low volatilities. In addition, there is a need for ink compositions suitable for ink jet printing containing solvents or humectants with high boiling points. Further, there is a need for ink compositions suitable for ink jet printing containing solvents or humectants that are highly compatible with a large number of colorants, cosolvents, and ink additives. Additionally, there is a need for ink compositions suitable for ink jet printing containing solvents or humectants with low viscosities. A need also remains for ink compositions suitable for ink jet printing containing solvents or humectants with high surface tensions. There is also a need for ink compositions suitable for ink jet printing which have low viscosities. In addition, there is a need for ink compositions suitable for ink jet printing which exhibit improved latency characteristics. Further, a need remains for ink compositions suitable for ink jet printing which exhibit improved frequency response characteristics. Additionally, a need remains for ink compositions suitable for ink jet printing processes employing printheads with small channels and capable of printing 600 or more dots per inch. There is also a need for ink compositions suitable for ink jet printing processes which are toxicologically and environmentally safe. Further, there is a need for ink compositions suitable for ink jet printing which generate high quality images on paper. Additionally, there is a need for ink compositions suitable for ink jet printing which generate high quality images on transparencies.